Can my ex sponsor another child for immigration purposes?

My ex husband and I have two children. Over a year ago he married a woman with dual citizenship in the US and Canada. The new wife has a six year old son. They have both been traveling back and forth to see each other but the kid wasn't allowed to leave while his visa was being processed. Now my ex says he has to go to Canada again to oversee his medical exam and meeting with immigration in Feb.(next month) because he is sponsoring the visa. His mother and I are both thinking he is just using it as an excuse to go back up there because she told him that she wouldn't help him out with my girls the next time he takes off with no good reason and leaves his real children for this woman and her son. Could my ex be sponsoring his "step child's" visa even though they never lived together?