In Win7MC I've been using the Tasks > TV > TV Signal > Scan for More Channels. It finds the new channels but doesn't change the previous Guide data. After the transition I will delete the C:\ProgramData\Microsoft\eHome\mcepg2-0 folder and completely reinstall 7MC. For sure, the Guide will not have the new channel info so this is probably going to be a mess. Maybe, please, Microsoft will finally enable ATSC in Canada. Zap2It has the data so I don't know what the hold-up is.
Samsung LN40A550, Asus A8N SLI, Athlon 64 X2 3800, XFX HD One 5450, 2 Hauppauge HVR-2250, LG BH10LS30 Blu-ray, Windows 7