Dear Rana,Asalam Alykem
First, McGill University has a course starts on May 5th
I do not know if you are in Canada or Libya. If you are in Canada you can apply and start On May 5th although you don't have CAQ (certificate from immigration office in Quebec). However, if you are in Libya you have to obtain CAQ to get Canadian Visa. As a result, it is difficult to start on May 5th, and it is better to apply for September.
If you have an admission from an institute in Montreal, you still have to obtain CAQ to get Canadian Visa.
Moreover, if you have an admission from any institute in any province in Canada except Quebec, you don't need to obtain CAQ, and
you can come to that province. Then, you can move to Montreal and start your English course. After that, you can apply for CAQ.
Give me more information about your situation, so I can help you
Regarding residence, I can help you when you arrive ,and there are some places where you can pay monthly for an apartment without any contract. Just let me know when you will arrive Montreal