Canvas Fields
Canvas Fields allows you to add standard Drupal fields, such as text or entity references, to Canvas Page entities. This integration helps content editors enrich Canvas Pages with custom data for use in Views, search, and other custom experiences.
Canvas Fields offers the ability to add normal Drupal fields to the Canvas Page entity. This allows content editors a way to add standard fields to the Canvas Page entity like text, entity reference, and list. This is useful if you want to create different Views, search, or other experiences.
Note that not all field types are supported, nor can they be. Also note that Canvas Page entity is not bundle-able (right now), so the fields you add will appear for all canvas page entity forms.
Multi-value fields will edit and save correctly, but on publish of a Canvas page, the form will not refresh reflecting your values. This is an open issue with Canvas. Simply reload the page after saving and it will show you the saved values.
Whatever the support winds up being for the future in Canvas, this module exists to add a bridge over for those who need to mix field and page builder experiences for different needs than purely presentation.