Cuirassier is a French unique heavy cavalry unit that is featured in Age of Empires III.
It is the strongest heavy cavalry among those cavalrys producible in the stable.
By looking at its ability, Cuirassier is just next after Spahi and equal with Dog Soldier.
However considering that Spahi is a limited unit which can be received with cards from Home City and the Dog Soldier is a highest top unit after dancing in the Fire Pit, it is very much advantageous since Cuirassier can be trained in the stable which its ability is equal with Dog Soldier.
Of course it is very expensive for the production of Cuirassier, but first you have to consider Coureur des Bois the French have that can afford its cost.
When Cuirassier reached its full upgrade, it possesses HP 1150 and Attack 66.
To stop such a formidable unit, the only tactics is to defend while disturbing the economic parts of French and also it might be useful to utilize heavy infantry since Cuirassier is a class of heavy cavalry.