Timeshifting in HD is possible. Problem is the network capacity.
So far, Vidéotron is in the process of either upgrade some areas to 1 GHz (like West-Montreal), or cut off Telemax analog (like Gatineau), or deploying SDV (Switched Digital Video), or a mix of them. During this process, they have to pick new HD channels by priority: the most popular channels, Quebecor-owned channels, and those channels offering unique programming.
Since 2 HD channels are taking the space of 1 analog channel, it just not worth it wasting 4 analog positions in order to offer ABC-NBC-CBS-FOX Seattle + SRC-CBC-CTV-Global Vancouver in HD when these channels offer exactly the same programming 3 hour earlier on their east-coast equivalent. A better usage of these analog positions would be to offer specialties broadcasting original programming that we're missing, like AMC, ABC Spark, Family, Food, HGTV, NASA, Showcase, Vanessa, etc.
Noteworthy, most of the movies on MExcess (except adult movies) also air at some point on The Movie Network main channel (M HD), same for MFun!, as well as Super Écran 3 HD and 4 HD, which might explain why they're missing.
Back on topic, there were rumors earlier this month that Télétoon (french) was about to launch in HD, which coincide with the addition of Cartoon Network and Adult Swim programming blocks being added to the channel this summer. No word about negociation status, but its carriage on Vidéotron is a big strategic one.
CM-3020 with CM-7777