I think a better comparison for Cantwell is Markell Bell.
Both have massive size, but had growing pains when they showed up.
Markel was ahead a bit due to his age and playing JUCO.
He played his first year, where he started 1/2 the year beside a veteran OG, which is very helpful for Communication.
Cantwell has better athletic traits, but remember its hard for a tall guys to learn how to bend and re anchor. Congdon is able to because of his wrestling background, hence why he may look better as an OG right now.
I think Cantwell will likley start next year at RT, and we can certainly stash him in the 2 deep while Buchanan and SJ play guard this year.
If they are just a touch better start them instead and keep coaching up Cantwell so you build up confidence and good habits and mechanics, ala Okunlola.