I get a travel allowance of $300/month in my salary - it is taxed. I use my car to visit employer stores . Can I claim car lease & maintenance on my taxes?

Does your employer provide you with a T2200 that allows a claim for expenses?
Since you receive an allowance, and reimbursement, it doesn't seem likely..)

Hi Tony - Thanks for reply.  I do not have a T2200 but my allowance of $300 per  month is taxed as part of my salary.   I leased a car for the job which costs ~$500/month + $1500 insurance/year and I use the car 75% for work to service my employers stores in Quebec and 25% personal use.  I am losing out on this equation.  Any recommendatons? - should I approach my employer for a T2200

You could ask for a T2200 but without this on file, you would not be able to claim employment expense. Otherwise, assuming your 25% mileage is reasonable, the calculation would involve lease costs, insurance, fuel, maintenance and licensing as you suggest.
If you were self employed, you could claim these costs as business expense, but it appears you are not.