Steve Sailer points to a NYT article on comparing the putative Hispanic authenticity of Marco Rubio and Ted Cruz.
Data on volunteered electoral preferences among Hispanic Republicans are scant. Reuters-Ipsos daily tracking consistently has a Republican/independent sample that is too small for Hispanics for the term to register as a identifiable category. I have been able to track down a couple of state polls in Georgia and Florida, both conducted in November, that have cross-tabs for candidate support and Hispanic ethnicity. Both consist of responses from "likely Republican primary voters".
In Georgia, Rubio gets 43% of the Hispanic support to Cruz's 23%. They get 8% and 12% of the state's total GOP support, respectively (keep in mind this was before Carson's precipitous decline began, back when Rubio and Cruz were a distant third and fourth). Yes, tribalism is everywhere--backing support among Hispanics out, we see that the two Hispanic candidates garner less than 20% of the state's overall Republican support, but 66% of its Hispanic Republican support.
In Florida, Rubio gets 23% of support from Hispanics of Cuban ancestry to Cruz's 9%. Among non-Cuban Hispanics, Rubio gets 9% and Cruz only 3%. Notably, Trump beats them both, getting 25% of Cuban support and 41% of non-Cuban Hispanic support in the state. Immigration from Mexico isn't a salient issue in Florida. Among all Republican Floridians, Rubio gets 16% to Cruz's 10%.
What do exist of the sparse data suggest that the ethnic pull is, at least currently, stronger with Rubio than it is with Cruz.