You'd need the U.S. to not restrict immigration form China with the Chinese Exclusion Act in 1884. Chinese immigration feel from a decenial peak of 133,139 in the 1870s to 65,797 in the 1880s and 15,268 in the 1890s as a result. Chinese immigration to the U.S. was limited to family reunification after 1884 and remained below 20,000 per decade until the 1980s. Keep in mind that until 1884 the majority of Chinese immigrants were male and were temporary migrants often returning to China. The exclusion act had the effect of keeping the men who were already in the U.S. from leaving and bringing their families over. An interesting aspect of the Chinese emigration was originally the vast majority of Chinese emigrants were from the Pearl River Delta.
For Italians, World War I and the subsequent 1924 Immigration Act put a stop to immigration. The Italian immigration to the U.S. had to compete with South America (Brazil and Argentina) as a destination for Italians from the Mezzogiorno and with Northern Europe for Northen Italians (few of whom chose the U.S.). Immigration from Italy was also dominated by single men, many of whom eventually returned, explaining why there were only 1.6 million Italian-born individuals in the U.S. by 1920, despite 3.8 million immigrants having arrived from between 1890 and 1920.
During the immediate Post World War II period, Italians emigrated in large numbers, but the quotas were not lifted by the U.S. As a result, Argentina, Australia and Canada all attracted larger numbers of Italians. Western Europe, Brazil and Venezuela to attracted large numbers of Italians during the 1950s. By 1965 when the quotas were lifted, Italy's economy had developed greatly meaning that Italian immigrant arrivals had been recuded to 150,031 in 1970-1979 and 55,562 for the following decade.
The easiest way to have more Italians and Chinese is to butterfly away the restrictions and the World Wars which would limit immigration.