You must mention all of the following (it is not optional):
WORK EXPERIENCE,
For the principal applicant:• original and up-to-date letters of reference from your past and current employers for the past 10 years.
Letters must be:• written on company letterhead,
• signed by the responsible officer/supervisor,
• show the company's full address, telephone and fax numbers, email and website addresses, and
• stamped with the company's official seal (if applicable).
Letters must include all of the following information:• the specific period of your employment with the company
• the positions you have held during the period of employment and the time spent in each position
• your main responsibilities and duties in each position
• your total annual salary plus benefits
• the number of hours worked per week
• a business card of the person signing
If you cannot provide a reference from an employer, provide a written
explanation and any documentation that would support your claim to such
employment and provide the information as set forth above.
For the accompanying spouse or common-law partner:• original and up-to-date letters of reference, including all details as specified
above.
in respect of any employment in Canada under a work permit:
• a copy of the work permit.
The source:
http://www.cic.gc.ca/english/pdf/kits/guides/E37048.pdf