My t5008 from Scotia Cap'l has no value in box 20, (cost or book value). Does this mean my entire proceeds of the sale of shares will be viewed as taxable capital gain?

On the T5008, you should make sure that the cost of the stock is shown in Box 20.  A lot of the T5008s issued this year do not show a cost amount in box 20 (usually because the broker did not have that information available) so you should check your own records for the details of the original purchase of the security and then enter your cost of the securities in Box 20 yourself.