So sometimes my friends and I play with two of the oversize cards and we ran into an issue using Harley Quinn and Deadshot and that is, which one do you have to use first?

So if you discard a four cost card, since Harley says you have to draw a card do you draw a card first before you stack a card from Deadshot, so you can stack that four cost card and then draw it again right away, who says you MAY stack a card or can you use it in any order because both of their effects activate at the same time. One happens to be mandatory and one is a choice which one do you have to do first or can you choose which to do first? Since this can happen in a normal game by using Jericho in Teen Titans I figured that I could ask for an official clarification.

Which one do you have to do first or can you choose which to do first?