From his "If I Made Another Monkey Island" post quoted in the ad:

> All the games after Monkey Island 2 don't exist in my Monkey Island universe. ...That doesn't mean I won't steal some good ideas or characters from other games. I'm not above that.

So it can be both! Monkey Island 3 is no longer canon (which is a shame because it's fantastic), but also Murray can be upgraded into the canon universe anyway (TV Tropes would probably consider this an example of a "Canon Immigrant").

A while ago Ron Gilbert laid out what it'd look like if and when he was able to make another Monkey Island game: https://grumpygamer.com/if_i_made_another_monkeyisland. He said he'd fork off the Monkey Island canon after the 2nd game, but also "that doesn't mean I won't steal some good ideas or characters from other games. I'm not above that." So I guess Murray (and using Dominic Armato as the voice of Guybrush) are part of that.

I was wondering the same. I love MI3 so much (first game in the series I played) but from a story perspective it just ignored the ending of the previous game. Would love to see Ron actually find a way to reconsile that instead of sweeping it under the rug.