To be fair the longest road tunnel in ottawa would be the underpass on prestone street.

the acoustics there are sweet but short lived. Great during Ferrari Fest tho. But late at night U can park under it and do sound stuff it resonates magnificent. I used to light off my boom cannon when I had my MX3 there.
Second best bet if you are going for sound would be to go to Place D'Orleans in their underground parking. Good Bang there too.
Cheers
Dime