How will I be able to use an iPad Air 2 when visiting England from Canada.

WIFi is WiFi no matter where you are in the world. As long as there is a WiFi network that you have access to and can connect to, you will use your iPad in England just like you use it in Canada. It will be no different all.

You shouldn't have any problems with WiFi in the UK.

There is no way to use a dongle with an iPad. You will need to connect directly to any WiFi networks that you can find.

I have never been to the UK, but here in the U.S., if I am staying at a hotel, WiFi is offered at an additional cost or in most cases it is offered for free. I connect to the hotel WiFi network just like I would connect to my home network.

Remember to get a UK adapter plug for your iPad so that you can charge it. There is one included in the Apple travel connection kit but you can also buy them separately from most luggage shops. Many stores at airports carry them as well.