Assuming you’re not

[Hatfield]

Assuming you’re not interested in rooting/jailbreaking your phone, your best bet is to go with a plan that allows tethering. There’s no need to switch wireless providers, just buy prepaid SIM cards and switch back to your AT&T SIM when you get back home. If it’s going to be an extended trip, ask AT&T to suspend your service while you’re away.

Googling “canada sim tether” and “uk france germany tether” got me these:

Canada: http://prepaid-data-sim-card.wikia.com/wiki/Canada

Also, the fine print states that T-Mobil’s prepaid SIM cards allow tethering in Canada: http://prepaid-phones.t-mobile.com/prepaid-internet

UK/Europe: http://kenstechtips.com/index.php/best-sim-cards-for-using-smartphone-in-europe