This is one of those 'what if' threads.
If they did eventually build a third gate it'd most likely go on the land to the east of the Sequoia Lodge and Newport (the Blvd. du Parc goes through the area).
My question is, would they have to create a new esplanade to the park? Its a fair walk from the Village and current esplanade, and you'd want day guests and hotel residents to be able to get to the park.
Perhaps Ave. Jules Verne (behind the Hotel New York) might be suitable, and there's a gap between the Lodge and Newport for hotel guests.
Other than that, I can't see there being much connectivity between this imaginary third gate.