It was with much disappointment that Media Center in both Windows 7 and the WMC TV Pack did not support ATSC for those of us in Canada, even with hacks such as this. However, former Microsoft MVP Peter Near described a potential workaround for this issue, as mentioned in his blog entry, ATSC, Canada, and Windows 7 - A Sliver of Hope, and worked with SiliconDust, makers of the HDHomerun ATSC product, to create a viable solution.
For more details, see Peter's latest blog entry on this issue, ATSC in Canada on Windows 7 - It's Here!, and this link on SiliconDust's support forum named ATSC OTA in Canada with WMC TV Pack or Win7.
Many thanks to both Peter and the folks at SiliconDust, for pushing to come up with a solution for us Canadians.
Note, this is not supported by Microsoft, but I'll definitely take what I can get. Once you have seen ATSC, NTSC just simply is not good enough anymore!