Other than the F1 broadcast SPEED really isn't in competition with TSN.
TSN and/or the US networks show the NASCAR races, SPEED only has extra race preview / review / update shows which are on either before the race/ after the race and during the week.
TSN has the IRL races too, although sometimes not live
What I want from Speed HD is the HD coverage of Rolex, LeMans, WSBK, Super-X, Barrett Jackson, etc, and even all of Speeds basic weekly shows, they are all natively done for HD now.
In Canada 98% of these races can only be found on Speed anyway, so there isn't any conflict with TSN or Sportnet that I see.