The regulated Canadian content is only on the Canadian Channels tat were added when XM and Sirius got approval in Canada. All the other channels are the same as in the US, including NASCAR 128 on Sirius. The only difference between Canadian and US subscriptions is that some channels in the US are blocked in Canada, to maintain a ratio of 1 canadian channel for every 8 US. With the US subscription you get all channels (incl. Canadian) with none blocked.

FYI
I broke down and purchased a Sirius Satelite system. You DO get the Nascar signal in Canada. It's a neat toy and I can't wait to travel with it. The signal is crystal clear. Apparently I should be able to pick up the MRN and PRN shows as well. We'll see. I'm listening to The Morning Drive Show right now. They're currently discussing the COT.