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Canadian immigration will want to know a number of things about your trip including:
The purpose of your visit
who is paying for your visit
If you have permission from your work to make the visit
That you will not be doing illegal work
They also need evidence to back up all these points. If you are travelling for work, a letter from your employer should help back up all of these, and so should state all of them. Stating what you are doing for them should cover the last point.