I imported the t5008 forms from CRA. Do I use them as capital gains or use the Schedule 3 to report Capital gains and this will include previous losses?

If you used CRA's autofill, you will need to edit each and every T5008 entry to make sure your purchase price is entered on line 20 and that the toggle switch is set to capital gains. 

No need to enter on capital gains Schedule 3 as the T5008 entries will automatically post to the schedule 3.