While most people want a straight up number... let me answer it this way...
There a several factors involved in how much 'weight' a magnet can hold. With regard to CanLoft... it has been specifically designed for cans, which are typically under 2 pounds. I've shown various 'feats of strength' in the project video to give an idea that the CanLoft magnet arrangement makes CanLoft work great for normal sized cans... holding readily and keeping the cans secure from accidental bumps, etc. Can they hold much more... sure, but that's not the intent as other factors come into play... such as the mounting, etc.
I've tested CanLoft surface on a variety of shelving over extended periods of time. In general, if your shelves (wood, plyboard, particleboard, mdf, etc.) are in reasonable condition, the one-screw mount of CanLoft surface works great. If you shelves are suspect... greatly bowed, deteriorating, unstable, etc... CanLoft is not suitable for use:)
Don't see the answer to your question? Ask the project creator directly.