Currency is the Canadian Dollar. ATMs can be found in most towns and accept all major credit cards. It is also fairly easy to change Euros, US dollars and Sterling.
English and French are the two official languages of Canada. French is the first language in Quebec and English in the rest of Canada. English is commonly understood in Quebec and most people speak it fluently.
Violent crime is not common in Canada and virtually unheard of outside of the poorer neighbourhoods of the major cities. The main danger you're likely to face is at the hands of the elements, and it's well worth fully checking out weather conditions before long winter drives and taking an emergency kit just in case you get stuck in adverse weather.
Visas are not needed for entry by UK citizens flying into Canada for tourism purposes.