The expression is “se tirer une bûche” in Québec, literally “to pull oneself a log”. Most often seen with the imperative form:

Tire-toi une bûche!

Not to be confused with “prendre une bûche” which means (see second tab) “to fall down/fall flat” (on one’s face) — generally “tomber”.

In the good old times in Québec, when people would meet and listen to story tellers, Ikea chairs were not invented yet and anyone who would come and join in the merry circle would be invited to grab a log and sit on it. Hence the “tire-toi une bûche” in lieu of “please take a seat”.