You asked about reps, not years of experience, so that's what I showed you - a direct comparison of how many snaps they took. Besides, all of that "experience" isn't quite what you make it out to be when you look at what he did and how long he was with those teams. For example, how much experience did he gain in the 36 hours that he was signed to the Bills? The only team he actually got any game experience with was the Arizona Rattlers. I wouldn't say he got years of experience kicking around like that any more than I would say Tyrell Ford got a year of NFL experience last year.
As far as his time as a starter goes, it started prior to Ottawa. Harris started 16 games with Toronto in 2015, when Ray was hurt so teams got a good look at him that year. He signed with Ottawa in 2016, and Burris had re-structed his deal so neither guy was making big money (for a starting QB) that season - they were both going to make around $250k + play time bonuses. Ottawa had structured both QB contracts in a way that it was clear Harris was the starter in 2017. Burris was going to make 200k in 2017 while Harris made 400k. Burris retired before the season so it didn't really matter in the end. https://3downnation.com/2016/11/24/henry-burris-trevor-harris/
Harris had led the league in passing TD's in 2015 with Toronto (was 3rd in passing yards too) so I guess that was enough for Ottawa to feel justified in the payout.