No, he specifically states that his attempt is to defend Christianity. In the leadup to the "wager," he expounds on the importance of the Eucharist and recognizing Jesus as God. He also contrasts the beliefs he argues for against those of the "Turks" (i.e. Islam).
That's irrelevant to his argument, he is saying, say Christianity is true and these things are important, then it's expected Muslims strive to find these truths. He is trying to make touring complete since other faiths belief in hell. So he is saying, consider these traits of Christianity as true, which he does believe is true but is besides the point. No Muslim should risk not knowing them in this case.
This is true.
If the last Prophet was Jesus (a), then Quran says it would be WRONG to follow Mohammad (s) because the former has proof and the latter would not, if Mohammad (s) is not a Prophet, Quran doesn't want you to accept him nor follow what you have no knowledge of.
Like I explained, this is part of how he covers all scenarios with his variable. You don't have to assume this variable is true, but he starts with say it's true. So that he has to show how this argument applies to other religions.