Mississauga or Oakville
Not sure what your budget is, how close to the church you want to be and type of cuisine.
I have had functions at Jonathon's:
They are great to deal with, the rooms are nice and the service and food is very good.
We have also had functions at Julia's:
It is also pretty good, but not as nice as Jonathon's.
Both are in downtown Oakville