I'm sure the tax code is Canada is similar to the U.S., but the difference is...
ESPP: the discount your employer gives is on the shares is taxable as if it were extra income.
then if it's not in a tax-sheltered account, you pay regular capital gains tax when you sell
Options: you will pay capital gains tax on the difference between sale price and strike price. (This is your most tax friendly option, but if stock price goes below the strike price your options are worth $0)
RSUs: are taxed as income, but even if stock goes down they'll always be worth what the share price is.
In the past Ive had the choice to direct a certain % of a bonus between options and RSUs. If you choose RSUs, a certain 'divider' was applied, I.e '5', so you could get 1,000 options or 200 RSUs.
At the time I was optimistic about my company, and therefore options seemed like the best choice. I was very very wrong, and watched the price drop below strike and stayed there for years. (The price almost doubled about a month after I left the company)