With ECN brokers (and Dukascopy is ECN) you don't have a shortage of liquidity providers, since ECNs are connected to the large external ECN pools with many-many participants, including leading banks, other brokers etc. That's what ECN brokers pay their "ECN subscription/connection fees" for.

That's why, unlike for STP brokers, where liquidity pools can vary in size and depth, with ECN brokers we don't have to worry about liquidity issues.

Dukascopy's MetaTrader is MT4 ECN.