4.5' seems a little shallow to me for the prairies. Code where I am is 5' and I know it can get colder out there. The local building dept can help you with that.
Wind or no wind you still need to anchor the building down to it's foundation.
Timberlinx are a fine product and certainly would do the job. The thing is they use a beefy threaded 7/8" rod that you would need to either install when you pour the slab (which would be a stressful exercise given the accuracy required and the impending setting-up of the floor) or drilling for anchors afterward while not drilling into the heating tubes.
Also remember that the post bottoms should not rest directly on the concrete. The end grain will suck up moisture from the floor. A barrier of some kind needs to go between the two.