Can I canvas with a service dog?

So I'm (37F) a canvasser, meaning I go into neighborhoods and knock door to door to get business for the company I work for. A little over a month ago I was attacked by a dog while working. In a nutshell, I knocked on a door that had the door open but storm door shut. I rung the bell and seconds later 2 dogs come running and push their way out the storm door. One dog paid me little mind and was probably just excited to be outside. The other dog (a pitbull) came right for me, bit my leg and calve 4 times then ran off when the owner came outside. Then as the dog ran back inside the house it attacked me again and bit my hand. This was very traumatic for me especially because this is the 2nd time I've been attacked by a dog (also a pit). After my first incident it took a couple years to be comfortable around dogs again. It was a process but I got over my fear. Hooooowever after my most recent attack I am really struggling with my fear of being attacked again. Particularly because I figured that's kind of a once in a lifetime situation but since it happened to me twice now I can't shake the fear that it's only a matter of time before it happens again. If I had a different occupation then I might not be so concerned but being a canvasser I am now on guard constantly at every door. I steer clear of homes that obviously have dogs and if there is one loose in a neighborhood I'm legit hauling ass and calling my boss to pick me up. I've had a couple sessions of therapy and will continue. I've been diagnosed with PTSD because my symptoms have persisted for over a month. So considering all this my question is.....

What are your thoughts on how having a service dog may or may not help me?

My thoughts... 1. I am normally not afraid of dogs so in a controlled situation and with a well trained animal I actually love dogs. 2. I am not looking for an "attack" dog because obviously I'll be in contact with dogs regularly and I can't have my dog just attack pets left and right. 3. But yes I want this dog to alert me to danger and protect if a situation arises where I need protection.