Generally speaking, condensation problems only manifest when moving your gear from/to a nice, warm interior to/from the cold outdoors. Once outside, once your gear has adjusted to the temperature, the concern is not nearly as great. The 7D is a professional grade camera, and as such is fully weather resistant. So long as you use professional grade lenses that are also weather sealed, and do not change your lenses while outdoors, you shouldn't have any problems with condensation building up inside your camera. You might still have to wait for any external condensation to dissipate before you can take any photos.
The real concern is when you have gear that is not weather resistant, and/or you need to change lenses frequently. When the weather is cold, it also tends to be fairly arid (moisture at freezing temperatures freezes and falls to the earth as snow), so simple cold is generally not a huge problem. When you encounter actual snowfall, windy conditions, etc. is when you should take particular care not to allow any snow, rain, or blowing particulate into your camera if you need to change a lens.
Finally, when you transition your gear from the cold outdoors to a warm interior, you will again have to worry about condensation. If you have fully weather sealed gear and never changed the lens while outdoors, you might find some condensation built up on the exterior, and dissipate as it warms. If you do not have fully weather sealed gear, then you should probably take some precautions to minimize condensation. Whenever I do any photography out in a cool humid environment or freezing temperatures, I try to bring my gear inside in stages, as I do not have fully sealed gear. I first make sure its all packed up in my camera pack, and leave it in a garage for a while (where the temperature is usually warmer than the freezing outdoors, but not as warm as my house.) I'll eventually move my gear indoors, where I leave it in my camera bag. I have several packets of silica in my camera bag, which helps to wick up any moisture brought in with my camera gear.
Once your gear is indoors, you should keep it in a dry place. Moisture built up inside your lens can result in mold growth, which can cause problems or render a lens useless. Professional cleaning services are available, but that usually costs something, and its always best to practice avoidance. If you worry that your lens picked up a fair amount of condensation even after carefully warming it up and bringing it inside via a camera bag, you might want to let the camera bag dry out before fully storing your gear.
