As an American, I feel that I grew up on the "Reduce, Reuse, Recycle" phrase, which applies here. Only later did someone eventually add "in that order", which made the entire process for me even more clear. And after some research, I find some of the European variations to be more accurate (though maybe less kid friendly...) http://ec.europa.eu/environment/waste/framework/index.htm
Reusing is going to be a better practice over recycling becauses it saves energy and costs at a lot of stages. You didn't need someone to transport the bucket to a recycling facility, transport those raw materials from the recycling process to a new manufacturer, incur the energy costs of manufacturing from the raw materials, and then the transport of the new bucket (or pot) back to a store for you to buy. (And this ignores the issue of Downcycling).
I think that the bigger issue that is hidden in your question is could there be an even better use for the buckets. Once you poke the holes in the buckets, they are only good for flower pots. Without the holes, you could still use them as watering cans or rainwater catchment, just to come up with a few gardening related ideas.
The entire premise here being that you are diminishing the overall value of the bucket by poking holes in it. In that way you are getting it closer to the point where recycling is the only option, since it won't work for a variety of other uses. In some ways this is inevitable, since pretty much everything wears out eventually and needs to be cycled as sustainably as possible.
The only recommendation would be to consider if there are intermediate uses for the buckets in between the restaurant use and your use as a garden pot. If you can use them for something and then as they get worn, use fresh buckets from the restaurant for that task and poke holes in the old buckets for pots, I would figure that would be a more sustainable cycle. Considering that your brother likely has a plethora of buckets, I would start there to handle your gardening needs over buying pots!