If they trade down, then I bet Kotkaniemi is a smoke screen because if they like Kotkaniemi enough to take him at 3, there's no way they explore trading down, especially not within the top 8. Considering the recent rumblings about Kotkaniemi not being out of place in the top 5, and there being so few centers high in the draft, there's way too much risk that someone else will take him if Montreal trades down.
It makes me think that maybe they like a few of the D, and with it being a D heavy draft, they can drop down a few spots and still get one of their guys. It'd be a similar but opposite predicament that CBJ was in 2015 when they explored trading up to 4 to get their D, but instead opted just to keep the assets because they felt between the three guys available, they were close enough that they'd take the one that fell to them.
The best case scenario for Montreal might be extorting a pick from OTT with the justification to OTT that they'd be blocking a trade down with a different team. Similar to when OTT gave up a 3rd because they really liked Logan Brown. I'd be surprised if Ottawa would do it because as of now, the team doesn't have a lot of 2nd/3rd round picks over the next two seasons.