First you decide where you want the canards to be, in the vertical and longitudinal axes, which is a complicated ballet of size, moment arm, area ruling and visibility, even before you get to canard/wing interactions.
Anhedral and dihedral may have something to do with the interaction bit, but more importantly, you don't want large gaps opening up at small deflection angles. I talked to one of the lead designers on Gripen last year, and he said that he caught a lot of flak for making the inlets square (versus oval on Viggen) but it was for exactly that reason.
Also, the "dihedral" on Rafale's canards is sometimes a factor of viewing angle:
http://kovy.free.fr/temp/rafale/rafale_show9.jpg
The Toom's tail anhedral IIRC was to get it out of a bad vertical location relative to the wing (pitch up issues) and I believe the Harrier's anhedral had too do with avoiding excess roll stability, although JF may correct me.