Welcome to FT.

1. Not really. It may be possible through various online conversion utilities and websites, but the fees will leave you feeling like you've been robbed (which would be entirely accurate). You're better to burn the points up, and begin collecting to Mileage Plus moving forward. To avoid being raped by scamcharges, burn your Aeroplan points by booking flights operated by United. It can be a pain to go through the US (unless you have Nexus/GE) but it's far, far better than being robbed.

2. Aeroplan's scamcharges = outright theft. Simple as that.

3. Yes, and probably in growing numbers if FT is any indication. Wouldn't you? Depending on one's travel patterns, some travelers have switched from Aeroplan to Mileage Plus, while others (myself included) have dumped Star Alliance entirely and moved to SkyTeam or OneWorld. It comes down to what works best for you and your unique travel requirements.

Given how Aeroplan has made it so much more difficult to earn miles (through instituting Tango fares on international routes, and charging major premiums to earn 100% mileage) as well as more difficult to spend them (by charging enormous premiums to use the miles you've earned, via scamcharges) the program no longer represents the same value to frequent fliers that it once did. It is entirely appropriate to investigate other options and ensure you're getting the best reward possible for your travel spend.