The problem for the Cats is the cross-over spot, where the fourth place West team has a better record than the third place East team (or vice versa). The Lions now have the same record as the Cats and are considerably hotter now. The Eskimos and Stampeders both have 7 and 4 records and are likely to have better records than the Cats at the end of the season. Now the Saskatchewan Roughriders have a 4 and 7 record after winning three straight and are only a game back of the Cats.
For the cross-over the other division team has to have a better record, i.e. in division teams tied on points get the playoff spot, so the Cats do have an advantage. However the upcoming "home" game in Moncton against Calgary has become more important. If the Cats win, they either tie or stay close to Montreal and hosting a home playoff game is still possible, especially with a game remaining in Montreal. If the Cats lose and the Riders win (although they're playing BC which complicates this scenario) the two teams would then be tied. Henceforth, if the Riders even end up with a single point more at the end of the season they would be in over the Cats.
Certainly this makes for more excitement in the league, and is part of the reason for the crossover. For the Cats it makes this next game against Calgary crucial. Win it and beating Montreal is still possible. Lose and the possibility of losing out on a playoff spot becomes more likely. Too bad the Cats aren't getting the full home field Ivor Wynne advantage this weekend.