I would never trust the airlines to handle my bike unprotected. They
don't call the guys that put the luggage on the plane "throwers" for
nothing. I've heard lots of stories of people getting broken bikes
back from the airline at the other end. After all, a bicycle is
pretty fragile. It's easy to break a spoke, dent a tube or bend a
derailleur hanger. To be fair I've also heard from lots of people who
had no problems.

Whenever I travel with my bike I get a travel case for it. The Trico
Iron case is awesome. You have to disassemble the bike abit. I have
to take off the wheels, the pedals and the handlebars. But once your
bike is in the case it is bomb proof. The Iron Case also has quite a
bit of extra room so you can pack other stuff in around your bike. You
can rent an iron case from Velotique in Toronto
(http://www.velotique.com/car-cas.htm).

If you are going to use a case, you might also consider sending you
bike courier instead of giving it to the airline. If you use the
'ground' service it can be quite economical. When traveling in Canada
its actually cheaper than paying the airline to carry a bike. This is
especially true if you have access to a corporate rate. I'm not sure
about going to the US. Ground takes about 5 days to go coast to coast.
I've used Purolator for this in the past and it worked great. I like
this option alot for several reasons:

1) Couriers seem to lose things less often the airlines.
2) You can track you bike. Once you give it to the airline no one
knows where it goes.
3) It saves you from having to lug a bike through the airport and
figure out how to get it from the airport to where ever you are
staying. In your case you could ship your bike directly to your
niece's house and have the courier pick it up there when you are ready
to come home and deliver it back to your house.

Hope this helps

Dave