ask for what? are you applying student visa? if so, they need the school offering letter - and your financial proof.
if you are talking about travel visa, they might ask you the employment letter and a return ticket.
you will have to be specific what kind of visa you are referring to before we could help you out
i don't have the experience, but common sense, will be
1. which company you are working
2. why you wish to work in canada
3. any job locally?
4. what you will do after the contract expired (normally work permit were issued based on your employment contract term, 1 yr or 2 yrs etc
5. you have any relative and family in canada
6. do you plan to migrate here
7. is the company provide you quarter or else are you planning to rent or buy a house..
8. will you bring your next of keens and kids over ?
above are the questions my friend was asked by the US Embassy when he applied work permit to go to boston to work