I take it by the "Possession and Acquisition Licence" that you're Canadian. Obviously, check what's legal first.

I have a Mossberg 590A1 and think it's perfect (for a social shotgun). One thing I can add is the Mossberg has a sliding tang safety on the top rear of the receiver (IMHO where it should be), unlike the Remington 870, which has a pushbutton at the rear of the trigger guard. The 870 is fine, if you're right handed. As for durability, mine's been through hell and still works flawlessly (at least so far). I bought the 590A1 because it's all metal, unlike the standard 590, which has a plastic trigger guard and other pieces. I'd recommend NOT getting a shotgun with a huge magazine. They just seem to make the gun too long and heavy, and I've heard of problems with magazine springs that long. Mine has an 18.5" barrel, ghost ring sights, a Surefire forearm light and a Sidesaddle (6 spare rounds). I don't believe it will accept the longer 'sporting' barrels, so that's something else to check.