How can I secure a canvas carport to a concrete pad?
To secure the base of the steel support you can use a concrete screw. TapCon is a ubiquitous brand TapCon screw that has worked well for me. You will need to drill into the concrete with the correct size bit (5/32" or 3/16") to accommodate the screw length. 

Another fastener type (Redhead is one brand) Redhead bolt is one in which after drilling a proper sized hole the fastener is inserted and then sharply struck with a hammer. The force of the hammer drives a metal shield around the bolt to expand outward which wedges the threaded post rigidly in the concrete. The machine screw threads can be used to fasten the base with SAE nuts.  Lastly, you can drill an opening in the concrete and insert a lead shield. This is basically a HD wall anchor. After tapping into the concrete a bolt is tightened into the shield it will  expand to tighten against the wall of the hole. 

Using a hammer-type drill with a masonry bit will facilitate the job of drilling into the concrete. I found when using expansion-type bolts that vacuuming the dust from the hole enables the expansion shield to hold and stay wedged as it is being tightened.