There is some degree of distinction, I'd say. Bisexuality is attraction defined by the male/female binary, pansexuality is attraction regardless of gender. A person can be bisexual and attracted to cis men and cis women, but not pansexual if they aren't attracted to trans or agendered folks.

Granted, a lot of people who say they're bisexual are probably actually pansexual, but stick with the label that is more widely used and understood out of convenience.