i'm late to this thread, but what are the approx dates in october? what do you both like to do?
the weather could still be really nice or cold, although the past few years it's been nice past thanksgiving. i live downtown, about a 15min walk from parliament hill and we walk everywhere - very walkable city (used to live in downtown toronto for years, can't even compare for walkability
gatineau park is amazing during fall rhapsody for the first half of the month - there isn't bus service to the best parts of the park, and the bike rental places shut down by then but you could consider renting a car for one day (we are car-free and sometimes rent a car for a day from enterprise as they often have local weekend specials for cheap if you are doing less than 100km a day even for just one day). champlain point is breathtaking at that time of year. there are other great spots that are walkable on the ontario side if you don't want to consider a car at all.
if you want to be close to the market the novotel is probably a decent choice as it isn't too noisy.
for downtown closer to parliament hill - minto place suites is good with great amenities and good kitchens. radisson, delta and albert at bay would all be reasonablr choices and close to parliament hill and within walking distance of almost everything.
transit is good in ottawa, with any of those hotels you'd be close to the transitway (tonnes of buses to everywhere in the city)
my favourite walk in ottawa is along the river behind parliament hill - it's gorgeous and not very touristed at all (i do the walk regularly). you can start/finish at either spot i'll mention. go toward the bytown museum (down the hill beside parliament hill and the last of the canal locks...continue down to the bottom of the hill and take the path for a gorgeous 20min walk to end either at the back of the natl library/archives, or continue to the war museum or even beyond. so lovely
for restaurants...again what do you like? if you stay at one of the downtown hotels you can head to where many of the locals eat on somerset or near somerset - upscale but with a fixed menu - zen kitchen, mid - tapas, inexpensive - ceylonta, tonnes of vietnamese places like ph bo go la. all you can eat sushi at yummy sushi is great. if you stay in a downtown hotel and want delivery for chinese - jo moon ting (hong kong style - don't order canadian chinese options), and seasons pizza - my bil is a fussy pizza eater from chicago and when they come to ottawa he always gets seasons pizza!). also on somerset is umi cafe (co-op) they often have live music...great space
in the market, i agree domus is a gem as is sweetgrass bistro. for inexpensive my faves are chez lucien and ahora. there's more but that's off the top of my head.
more suggestions if you'd like if you have any specific questions.
mama to callum (april 8,07) and everett (sept 24,09) - blessed to be married to my life's love since '98.