For some reason I though it would be a bit more serious, lol.
Roy and Riza's relationship IS canonical. You see that they have feelings for each other during the series. From the outlook their feelings seem mutually just professional, but they do hint at something different. The thing is, they didnt elaborate on their relationship enough so you can only guess their future by the end of the Shambalala movie. But a Roy and Riza's relationship sounds logical, just dont go too overboard with the romance