Nowadays there are tons of online print shops. All of them offer you to print your photo in the best possible quality on canvas, alu dibond or acrylic glass. If you look closely though, there are huge differences in quality.
First you have to diferentiate between two very different printing techniques. Some print the photo directly on the alu dibond or acrylic glass plate, others print the photo first on photo paper and laminate the print in a second step on the alu dibond or acrylic glas. Direct printing results often grainy photos simply because this method is not yet technically mature. Especially on darker pictures you can easily count the pixels. So, if you can choose the second option. It is definitely worth the slightly higher price.
When we decided to do Photocircle, we also had to decide between those two different printing techniques and became experts in this field. Because we work together with great photographers from around the globe, we quickly decided to offer only laminated prints.