Rubrics will import / migrate from Blackboard, however they may not look the same way they did in Blackboard. This will depend on how they were set up in Blackboard.
Rubrics in Blackboard go from worst-to-best, in Canvas Rubrics go from best-to-worst.
Note: Depending on the Blackboard rubric criteria and set up there could potentially be a good bit of rearranging, copying, and pasting that will need to done to fix the rubric import to Canvas. It might be easier to build the Rubric in Canvas from scratch, however if your Rubrics are text heavy in Blackboard with long descriptions and information, this method and the time spent will work well as the text will be in the correct order in Canvas.