Mounana qualified for the third round after beating Zambian outfit Power Dynamos 4-3 on aggregate.
Bucs, who almost threw away their one goal advantage before drawing 2-2 with URA, also advanced to the next round on a 4-3 aggregate.
Pirates and Mounana will meet in the first leg in Gabon next Friday, April 17, before playing again in the second leg on Friday, May 1.
The winner of this tie will go through to the final round of the Caf Confederation Cup qualifiers.
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