If the gun is purchased on Monday, the law comes into effect on Wednesday and the item makes it across the border by 11:59pm on Tuesday then I would say "No". From past experience and reading other IRG posts (I could be wrong so I would wait for their reply) they seem to transfer the gun to their Canadian store and then right after that to you before it leaves the USA, but the finalization of applying all applicable Canadian laws seems to happen at crossing the border.
So, simply put, if it can get across the border before the new Canadian law is required to be used by IRUNGUNS, then that law won't be applied to your purchase.