No. Ethnic Ukrainians make up a majority 62% of the city of Odessa's population. Ethnic Russians are 29%. This according to the last census.
And Odessa Oblast has even a higher percentage of ethnic Ukrainians and lower percentage of ethnic Russians.
There WAS a Russian majority until WWII and the regions assimilation into the Soviet Union. Then many Ukrainians migrated there.
But it look like Russia stole it fair and square from the Ottoman Empire:
During the Russian-Turkish War of 1787–1792, on 25 September 1789, a detachment of Russian forces under Ivan Gudovich took Khadjibey and Yeni Dünya for the Russian Empire. One part of the troops came under command of a Spaniard in Russian service, Major General José de Ribas (known in Russia as Osip Mikhailovich Deribas), and the main street in Odessa today, Derybasivska Street, is named after him. Russia formally gained possession of the area as a result of the Treaty of Jassy (Iaşi) in 1792 and it became a part of Novorossiya ("New Russia").