You should contact the Ontario Ministry of Transportation (MTO) to find out for certain if you can apply for a G2 at this time or must obtain a G1 (which is like your learner's license from Saskatchewan) and then move up to the G2 in time.

According to the Ontario Ministry of Transportation site if you are a new resident of Ontario and have a valid driver's license from another province or country, you can use that license for 60 days in Ontario. If you want to continue to drive after 60 days, you must get an Ontario driver's license.

All applicants for an Ontario driver's license are required to pass a vision test and a written knowledge test regarding Ontario's traffic rules, pay all applicable fees, and provide acceptable proof of identity. Applicants who fulfill these requirements can obtain a G1 license.

The MTO also notes for other Canadians that if you move into their province and you have less than two years of driving experience, you may get credit for your experience for graduated licensing and be issued a Class G2 or M2 license. Once you have a total of two years of driving experience, you may take the G2 or M2 road test to earn full driving privileges. However since you still have your learner's license from Saskatchewan you should contact the MTO to see if you have to take the G1 road test first to obtain the G2 likely you will since you learner's license would be on par with their G1 license.

If you hold a controlled class license from a Canadian province or territory, once you are eligible to attempt the G2 road test, you must pass the road test within one year of the license exchange to be issued the equivalent controlled class license. If you pass the G2 road test after one year from the date of exchange, you will be issued a class G license.