If you stick with flint, there is absolutely no problem having kits shipped in from the States direct to you. Both the US and Canada do not consider flint lock rifles to be real guns, so there is no restriction on ownership. And, if they are of U.S. origin, there is no duty. You will have to pay PST &GST. There isn't much problem bringing any gun parts into Canada as long as it isn't a receiver for an automatic weapon. Of course, for any thing but flint, you must have a PAL card. Except for flint, the US does have pretty stiff firearm export regulations & it may be difficult getting someone to ship to you.
For the complete lowdown, go online to check the Canada Customs gun import regulations. If you still have questions, phone the gun registry people. I have always found them to be very pleasent & helpful.
Most of the ML dealers it the US are familiar with what they can do as far as Canadian regulations are concerned, because they already have experience shipping to Canada.
So, no more excuses. Jump right in & welcome to the dark side.
Paul