Virtually the same rule applies in Canada and in the United States.

The rule is that in order to provide fairness to the parties, and to not allow one judge of the same level to over rule another judge of the same level, once a judge has begun to hear a matter that same judge continues to have jurisdiction over the matter until its ultimate conclusion in that level of court.

In the case of R. v. Macdougall, File No.: 25931., [1998] 3 S.C.R., in paragraph 67, the Supreme Court of Canada clearly stated:
"...the usual rule that the judge seized of the case retains jurisdiction over it until its conclusion."

How a judge becomes seized of a matter has been common legal knowledge for centuries; just ask Google.:

The facts that Judge Kaufmant:
(1) heard the declaration evidence on the matter; and
(2) made a ruling on the matter; and
(3) stated that the best way for the case to continue was to file a new statement of claim; and
(4) gave advice on what research to do in order to prepare the new statement of claim,
           meant that Judge Kaufman was seized of the matter.