One product in multiple categories
There is no enforcement in Drupal Commerce of any product catalog data model. The solution will depend on how you've configured your taxonomy vocabularies, really. If you have a single catalog vocabulary, simply add a multi-value taxonomy term reference field to the node type you're using to display products. This will let you assign as many categories as you want per product page.

When it comes to actually creating a View of the products, it isn't clear what you're attempting or why. A single View should be able to filter a group of nodes to any selection of or combination of taxonomy terms. You may need to export the View or paste a screenshot of your configuration to this question to get more specific help.