According to Google Search, "if it wasn't for you <verb>ing" and "if it weren't for you <verb>ing" are both used.

What is the correct usage of wasn't or weren't in this case?


In English the Past subjunctive mostly has the same form as the normal Past (indicative). That's why Pt* (Past subjunctive) is only used with special indicators, after words as, for example, "if, as if/as though" + would in the main clause. The only verb that has special forms for Pt* is to be:

Past was/were/was - were/were/were, Pt* were/were/were - were/were/were

But as Pt* has mostly the same form as normal Past, in colloquial speech the genuine subjunctive "you were*" is mostly replaced by "you was". This is a bit earth-bound and in more elevated style you still use the proper subjunctive "you were*".