a pug is a little dog... are you going the portrait look or the running in motion look??
portrait look - i personally would try 85 on a 5D -- I personally would favor the primes as the thin DOF look is what makes pet shots (in my view) also take the 35 - i know with my dogs i usually have to be pretty close for them to sit still... within reach with food for example. For this the 85 might be a tad long... dont worry about slight distortion close up... dogs arent as picky with their portraits...
For running around... definantly try the 70-200 ai servo and 3fps. If you have to try f4 if the 5d focus isnt keeping up - it can - ya just have to nail it when in servo. I tend to shoot centre focus point as its accurate and fast and if i have to recompose - i do it with a slight crop.
Main thing is - if the dog is a foodie - take something they never get to eat thats a favorite... it sounds stupid but my dogs do anything for any food... and more for something like cooked chook or snaggas. (sausage) The owner hopefully will be able to keep them still and if you can get them to look down the lens - awesome...i often call my dog while looking in vf and he tends to look right down the lens - but only for a second then looks away... holding food on the hood with my left hand helps...
and making a screaching high pitch sound makes many dogs tilt their heads and perk their ears up... you might look like a fool but youll get the shot 
Goodluck! have fun...
(yeah i had dogs when i bought my cameras - now attention goes on the 1 year old bub)
Not my dog - but this is 50mm on a crop (80mm) and is a small dog - jumped up between my legs.... so only about 30cm (1ft) from the lens id say. this is f1.8... red picnic rug comes out pretty cool -

and this was when i first got my 50 - f2 my dog - wasnt meant as a portrait - just me mucking around (no effort)
and my other pet...
haha nah just kidding. (and this has nothing to do with this thread - its f5.6 400mm on a 40d)