Right now, the distribution of seats in the Greek Parliament is:
- Rulling coalition (New Democracy & PASOK): 152
- SYRIZA: 71
- Golden Dawn: 16
- Independent Greeks: 13
- Communist Party of Greece: 12
- DIMAR: 11
- independents: 25
Golden Dawn and the Communist Party will most certainly not support the government's candidate. Nikolaos Michaloliakos, GD's leader, was arrested in September 2013 and is still imprisoned (pending trial), along with other prominent party members. GD has accused the government of persecution and it's extremely unlikely that they'll do them any favours.
The Communist Party of Greece considers itself the polar opposite of the ruling coalition, and has a very long history of not co-operating with any other party (even left wing parties). It will be a very big surprise if they support the government's candidate.
Alexis Tsipras, SYRIZA's leader, has already stated that they won't support any candidate. This isn't a surprise, SYRIZA has the most to gain from premature elections. As you've mentioned, they won the recent Euro election, and are leading most polls. Unless something changes dramatically, they have a real chance of winning the next elections.
Thus, the government will have to seek the 28 votes they need in a pool of 49 voters. It could really go either way:
- The leader of Independent Greeks, Panos Kammenos, has - very strongly - stated that they won't support the government's candidate. However, the party's MPs have not always followed their leader in the past. A handful of the 25 independent MPs are former Independent Greeks that left the party after clashing with Kammenos.
- The leader of DIMAR, Fotis Kouvelis, has stated that he doesn't think the parliament will be able to elect a president.
If we take the opposition's statements at face value and all their MPs follow the party line, then the presidential election will fail. If that happens, then the government will have to dissolve the parliament in at most ten days.
However, there's really no way to guess how any of these 49 voters will vote. On top of that, I can't say categorically that all SYRIZA's MPs will oppose a left leaning candidate. The goverment has already approached Mikis Theodorakis (he denied), so the scenario of a candidate with ideological ties to SYRIZA isn't that far fetched.
Only time will tell.
The third round of the presidential election (Dec 29) failed to elect Stavros Dimas. The general election is set for 25, January 2015.