it is really important that you know WHAT you are going to be using the cage for, and taht you make sure it meets all of the requirements.
to help your eventual re-selling of teh car, you should also look to have a cage built that will meet the regulations of as many disciplines as you can. A rally cage, with a dash bar and nascar style door bars woudl be legal for WCMA racing (in fact a bit overbuilt)
Bolt in cages, by their very nature, don't fit well in the car. There are usually relative large caps to the shell and whil they will protect you, the body gets much less stiffening from them.
Custom building a cage is expensive when done right ... but you get a LOT from it.
Jackson Motorsports is probably the place to go in Winnipeg, and Guyons Performance Centres in Calgary is who I use here.
Check with the local competitors and see who they use...