Actually, that isn't the point. Since he is Canadian, he can start the application process while he's still in the States . . . . but only if they apply outland. Also, applying inland means that applicants forfeit their right to appeal a refusal - and this is really important. Inland should only be used when there is an advantage to the applicant, for example, when they are from a non-visa-exempt country and are in Canada illegally, or when they are non-visa-exempt and are not in a position to travel home if there is an interview (because non-visa-exempt applicants for PR will not be issued temporary status to come back to Canada if they leave.) Inland vs outland is NOT about where the applicant is staying during processing, so you can't just say "Apply inland if you want to be in Canada during processing, or outland 'if you want to settle things before moving'". It's just not that simple.
In addition, there could easily be problems with the daughter because of her age. She is a legal adult - and there can be complications associated with that. Just take a look at my signature timeline - all the result of an inadmissible 19 year old son who was not in Canada, and who wasn't even coming to Canada in the first place. People should not just give up their appeal rights - not unless they have to. You never know when an application can just go off the rails and, if you're in Canada applying inland and the ap is refused, you're gone.