If I use an English mobile phone in Canada to call a English landline in the United Kingdom using an international calling card, will I be charged extra by my phone tarrif? The phone is on Vodafone.

Almost certainly!!!! Local Canadian numbers would be £1.35/minute and, even if the calling card has a "free" (from landlines) 1-800 access number, I see nothing that these would be charged any less!

The above above seems spot on.

The calling card would only be useful in conjunction with a local SIM.

Canada is NOT a good country for that either! There are no cheap PAYG SIMs as in the UK. Visitors can, with some effort, get a 1-month minimum prepaid local contract. But then they might be as well to call the UK using it!

if you have a smartphone and access to wifi you should be able to use that to make some cheap calls via skype or simler