The main thing that will determine if Rogers Centre or BMO open up is 2 fold:
1) Are they just going to open to the teams to play
2) Will there, and eventually how many, fans will there be in the stands
For #1 there is an added factor for all levels of government to consider:
The Toronto Teams are in Florida, and many members are American citizens (or have US green cards to play) ... this means that within the next month they will all be vaccinated via the US efforts.
As long as the majority of the teams get their shots then I think the Jays and TFC are back by June with no fans in the stands (and of course still following Canadian public health guidelines/League guidelines when they are here)
Both TFC and the Jays have an advantage in that they have accommodation for the visiting teams that will keep them close to where they are playing (with certain amenities).
As for #2 - Fans going back in - I don't think we'll get there this year (just to be really cautious and account to any other issues that might creep up).