Canadian ad rates confuse the hell out of me but I'll tackle what this means. The Grey Cup and Super Bowl draw similar Canadian TV Audiences (right around this 4M number as well). The Superbowl ad rates in Canada has ranged from $90K to $130K for a 30 second spot, and Grey Cup has been between $40K and $65K from rates I could find. In 2014 game 7 of the Habs and Rangers drew about 4.5M. Oscars don't appear to have listed Canadian ad rates but it draws about 8M (in the US it's about $1.9M for their 40M viewers).
I would guess that this 4M is a bit of a surprise to the Sportsnet brass so they won't see an increase in rates until this game, and next series should they get there.