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We have multiple eCommerce sites which not only share products across domains but also across categories within a single domain.

Examples:

http://www.artisancraftedhome.com/sinks-tubs/kitchen-sinks/two-tone-sinks/medium-rounded-front-farmhouse-sink-two-tone-scroll

http://www.coppersinksonline.com/copper-kitchen-and-farmhouse-sinks/two-tone-kitchen-farmhouse-sinks/medium-rounded-front-farmhouse-sink-two-tone-scroll

http://www.coppersinksonline.com/copper-sinks-on-sale/medium-rounded-front-farmhouse-sink-two-tone-scroll

We have selected canonical links for each domain but I need to know if this practice is having a negative impact on my SEO.