It depends whom you petition. If you petition the House to call an early election, that's part of our normal democracy. If you petition the army to remove the government, that's attempting a coup.
In this case the MoU was not petitioning the House to call an early election, it was petitioning the Senate and Governor General to call an early election, who do not have the legal authority to call an election while the government has the confidence of the House.
And whether it's conditional on your demands being met is irrelevant. You can't hold a gun to someone's head and tell them to do something, and then say "well I was only going to fire if they didn't do it". The problem is in the threat, not the ask.
I just read the MoU (https://web.archive.org/web/20220122173201/https://canada-un...). It is a ridiculous document, suggesting that CU and the central government will form a joint committee to set Covid policy together. But nowhere in the document do I see anything about calling an election, dissolving the government, or being beyond any constitutional powers. The Wikipedia quote upthread does not seem like an accurate summary of the MoU.
Obviously it takes some suspension of disbelief to take anything in that document seriously, but it suggests that the Senate and Governor General (both unelected) make up the new "Government of Canada", with no mention of the House (elected). It's pretty clear that the intention of the "offer" is to remove the duly elected government from the picture in the mistaken belief that the Senate and GG are of higher authority to the House.
As far as the petition for an early election goes, I agree I can't find it in the MoU. Perhaps it was reading between the lines and combining statements made outside the MoU with what was found within.
Petitioning for early elections (even if impossible legally) is a far, far cry from "overthrowing the government"*.
Would you be willing to edit your original post to provide some context here?