Go chat with our Cdn barrel makers to see what they can do for you in making blanks. From there, you can machine for final fit. I think that is the easiest way as rifling requires quite specialized equipment.
If the volume is large enough, then it is worth doing the import thing. Either finished barrels in bulk or blanks for final machining.
Personally, for what market there is in Canada, I would just go talk to a major US supplier, import a bunch at wholesale pricing and sell them. Unless you are making your own barrels within the expected market costs, you will face a hard sell.
There are a number of 'generic' barrel makers that do their stuff under the lable of a big boy. Maybe they will make for you under your lable is you meet their min.
Remember that making a gun part also requires liability insurance. That is very expensive.
Jerry