I never realized that we get to choose what pact Wyll has despite it already being established, funny.
Do we get to pick his pact? Or his patron? Warlocks are a bit unusual in that they have two types of "subclass choice" whereas most classes just get one. Patron is chosen at the time the character is created, and as far as I remember Wyll has infernal patron. IMO the patron choice should be locked in for Wyll because the details of the patron are quite likely plot relevant.
Pact is chosen at level 3. As of the last time I played (which was some time ago) only pact of the chain was in the game. The players hand book also has pact of the blade and pact of the book.
You may be referring to the fact that Wyll's sobriquet "Blade of the Frontier" has the word blade in it, but I am not convinced that this should lock him into blade pact. Wyll is full of shit, so making up a story about being a good swordsman when he very clearly is not seems to be in character. You could probably make any of the pacts work with Wyll (although his stats are terrible for blade pact).