If the roads are travel worthy then take a drive to Sydney because the birding is great all year round.
Donkin is a migratory point that is only about a half hour from Sydney, with the Glace Bay Bird Sanctuary very close by.
An easy and low kilometer route to guarantee a variety of birds is to drive out the Louisbourg Highway and cross over at Birch Grove into Port Morien. There is a sandbar and salt marsh in Port Morien and from there you can zip on to Schooner Pond in Donkin. They are you can hit the Sanctuary on the way home and go back through Glace Bay, maybe even hit the airport on the way home where birds seem to come in for their own landings.
The surrounding areas have lots of other hot spots but this is an easy day trip if you spend the night in Sydney. Most of the accommodations and eateries (check out Flavors, Governors Pub, and Doktor Lukes Coffee) are going to be in Sydney if it’s a non-touristy time of the year so for a winter trip in particular this is a good route to go. October would be the peak for everything, hands down but you have to go with the seasons to see what nature has to offer.
Cape Breton has lots of other good birding areas or course.
If winter birding is not your cup of tea, you might want to consider the fact that a good sized group of Barrow’s Goldeneye ducks hang out by the Dobson Yacht Club and in towards the Coxheath Bridge in the colder weather.