In the US it's often been used (& touted) as "vaccine substitute" for those who for ideological reasons didn't want a vaccine (and then got infected). However that's not how monoclonal antibody [MAb] therapy is to be used, according to the Canadian press & authorities. To quote from the Nov 3 article found by markvs:
The Ministry of Health said on Wednesday that 1,209 [MAb] doses have been allocated to Saskatchewan and the province has received 476 so far. To date, one person has received the treatment in Regina and five in Saskatoon. [...]
Monoclonal antibody treatments only work on patients who have no or very low levels of antibodies — meaning most vaccinated people wouldn't qualify — and should only be used in the early stages of a mild to moderate COVID-19 infection, within five days of becoming symptomatic.
The treatment is also aimed at people who are 55 or older and have not been vaccinated, or are immunocompromised or immunosuppressed. In some cases, patients 18 years of age or older might be able to receive the treatment if they meet specific high-risk criteria, according to the province.
Whether they are rationing it too much, it's probably going to be a matter of opinion.
The UK for example, only started using it in Sep 2021 and with a similar indication (as Canada), which should give you an idea how "socialized medicine" views it, more broadly:
Ronapreve, an antibody cocktail developed by Roche and Regeneron, will be initially used to treat COVID-19 hospital patients who have not developed an adequate antibody response.
It will be provided to those without antibodies who are aged 50 and over, or those aged 12 to 49 who are immunocompromised, including people with some types of cancer or autoimmune diseases. [...]
Antibody testing will be used to determine whether patients are seronegative, meaning they do not have an adequate existing antibody response and could therefore benefit from the medicine.
Risk of death in severe cases was reduced by about 20% using the treatment according to that Sky article (which doesn't cite clear source for that data though). Wikipedia, citing the actual clinical research, makes more clear who benefited the most in the trials (20% of 30% is 6% absolute difference, so it's probably the same trial data being referenced in both sources):
On 16 June 2021, preliminary form the Recovery trial showed reduced mortality from 30% to 24% in patients that had produced no antibodies themselves which were 33% of the total of participants.
If you look at the actual trial paper preprint, there was no statistically significant difference in the other groups, or even an overall effect...
In an analysis involving all randomised patients (regardless of baseline antibody status), 944 (20%) of 4839 patients allocated to REGEN-COV and 1026 (21%) of 4946 patients allocated to usual care died within 28 days (rate ratio 0·94; 95% CI 0·86-1·03; p=0·17). The proportional effect of REGEN-COV on mortality differed significantly between seropositive and seronegative patients (p value for heterogeneity = 0·001).
I would guess it's for reasons like this that other countries' regulatory agencies haven't followed the FDA in giving Regeneron's treatment the broader prophylactic recommendations that the FDA gave.
Actually the FDA itself says something rather more reserved in terms whom should take the treatment, but still broader than the Canada or UK criteria, in that no explicit serologic testing is involved in the FDA recommendation:
REGEN-COV may only be used as post-exposure prophylaxis for adults and pediatric individuals (12 years of age and older weighing at least 40 kg) who are:
at high risk for progression to severe COVID-19, including hospitalization or death, and
not fully vaccinated or who are not expected to mount an adequate immune response to complete SARS-CoV-2 vaccination (for example, people with immunocompromising conditions, including those taking immunosuppressive medications) [...] and
have been exposed to an individual infected with SARS-CoV-2 consistent with close contact criteria [...] or who are at high risk of exposure to an individual infected with SARS-CoV-2 because of occurrence of SARS-CoV-2 infection in other individuals in the same institutional setting (for example, nursing homes or prisons)
The FDA is (interstingly) merely citing PCR confirmed infection reductions, rather than any more serious consequence reduction...
An 81% reduction in confirmed symptomatic COVID-19 cases was observed with REGEN-COV compared to placebo at day 29 in cases who were RT-PCR negative and seronegative at baseline (the primary analysis population). In the overall trial population, there was a 62% reduction in RT-PCR confirmed symptomatic COVID-19 cases in the REGEN-COV group compared to placebo at day 29.
The FDA doesn't explicitly cite any reduction in deaths or even hospitalizations; I'm guessing the FDA merely assumed these follow from the lower rate of infection.
So I guess one could say there is some philosophical difference in how to interpret (that) trial data between various regulatory agencies... observed reductions in severe outcomes (and just in some sub-population) vs what would follow in theory from the reduced infections.
There is perhaps some similarity here with the cost-effectiveness disputes surrounding prophylactic use of Palivizumab (a monoclonal antibody treatment for RSV in children): "Results varied enormously, [...] and the majority of studies did not reveal cost-effectiveness except for subgroups of high-risk infants. [...] Recommendations for palivizumab prophylaxis differ by far from country to country. [...] discussion concerning the high costs of the product and its incomplete efficacy remains to be a never ending story." Canada for example has been among the countries that have revised their guidelines (in 2015 for Canada) towards less use: "There is evidence that the risk of RSV hospitalization does not warrant the use of palivizumab in many infants for whom it was previously recommended." Then a 2020 study (funded by the drug manufacturer) found that Quebec should have added [at least] two more (gestational age) weeks to their guideline for palivizumab in preemies, etc.
Keep in mind that some people die of Covid-19 not only because of too little immune response but sometimes because of too much of the wrong kind: cytokine storm etc. According to Healthline, cytokine storm can also be an unintended side-effect of monoclonal antibody therapy, so it needs to be administered in a well-monitored setting.