- Have you ever used a Canon or Nikon DSLR before.
- Do you already have a Canon or Nikon SLR
- Do you already have lenses for a Canon or Nikon SLR/DSLR
If the answer to any of the above is Yes... then go with what you're already somewhat familiar with.
If not and you're totally new to the field, then it's a complete coin toss as to which manufacturer you chose.
I use Canon so I can recommend them. Other people here use Nikon and will recommend them instead. To be honest, it really doesn't matter.
Go into a camera store and physically hold each camera. See what feels right in your hand. Play around with both of them. Some other things to consider might be
All my friends have a <BRANDNAME>" - in that case, you'll be able to borrow lens from them and learn from them
Store Rebates, maybe there'll be a deal in a store/online that'll allow you get one cheaper over the other
IMHO though, for an entry level camera, it probably doesn't matter all that much. Just be aware that if you get seriously into photography over the coming years, then you'll probably end up sticking to the manufacturers brand you chose today, as you'll have bought lenses & accessories for that manufacturer.