What is the nicest area as far as weather, lifestyle, etc. in Canada in your opinion?
When it comes to weather you're gonna have to pick your poison. It's either B.C and deal with the constant rain in the winter months or deal with colder but sunnier weather of places like Ontario, Quebec and Alberta. Out of those last three I mentioned Ontario has the mildest winter but in Alberta you can get warm days of up to 70 degrees in the winter brought on by something called chinook winds but they only last a few days.
Wrt the other stuff I guess you have to weigh what is really important to ya. If you're into nightlife, restaurants, and plenty of festivals you'd have to go with either Montreal or Toronto. Problem with Montreal is that to really get ahead career wise you need to know french. Btw, its not that the other cities like Calgary, Edmonton, and Vancouver don't have these things but it is very limited when compared to Toronto and Montreal.
If you like the outdoors and doing stuff like hiking and mountain biking than Vancouver would be the place to go. Just don't expect a vibrant city and great weather.
Calgary is growing but its considered Canada's Texas so make of that what you will.