You can train any plant into an espalier if you start early enough and are a dexterous pruner :-) But some types of plants just lend themselves to this practice better than others. I wound not consider either an azalea or a hydrangea shrub very well suited to this just by virtue of their growth habit. But I am sure someone with the patience and skill could manage it!

Thanks so much! I wont do those guys then :)