Hey Guntaker,
I know Mopac Auto Supply carries Borla products. They are a little expensive but cheaper than shipping from US.
Mopac
They're at 76 and King George in Surrey
Also check with Lordco, they carry quick a lot of HiPo stuff.
Some guy from Montreal had a cat back Bosal system FS. I emailed him but he never responded.
Any shop can install a cat back system. Custom is another question. I know one guy had a custom system made for his SVT made at a Midas shop on Main. (I think)
Cheers