1. Pronunciation is different and accents are different.
2. Words have different meanings. First example that comes to mind is the adjective plein(e). In Québec, when a person says it, it can mean they are full of food, whereas in France, it means they are pregnant!
3. Expressions are different. You have Québec idioms/proverbs that mean not very much to a Parisien French speaker, and vice versa.