Mustard seeds Europeans are the biggest market for the brown mustard, while Americans consume mostly yellow mustard, but one this is for sure, both varieties get their start in Canadian soil Canadian Mustard Seeds are known for its quality. In Canada Mustard is mainly categorized into 4 Grades: No .01 Canada No. 02 Canada No.03 Canada No. 04. Canada Domestic Mustard seed is Classified as: Domestic Mustard Seed, Yellow, Canada comes from white/Yellow mustard plant with Approximate size from 2 mm or less in diameter, Shape: Spherical or Oval. Domestic Mustard Seed, Brown, Canada comes from brown Indian mustard plant with Approximate size from 2 mm or less in diameter, Shape: Spherical or Oval. Domestic Mustard Seed, Oriental, Canada comes from black mustard plants with Approximate size from 1.2 to 2.0 mm in width & 1.6 to 3.0 in length, Shape: Oval.