You know Trump has a better record in open primaries, right? If your theory is correct, they seem to be trying to give us Trump, not Cruz.
I have looked at the data in Ohio and I'm utterly convinced that there was heavy Dem crossover for John Kasich in areas that are known to be Democratic strongholds, Cuyahoga county and Franklin county for example. Dems elected John Kasich in Ohio and it was reported on but widely ignored by the media.
And this is interesting as well: Dems Think Crossover Voters Helped Kasich Win GOP Primary
If you look at the Wisconsin Republican primary numbers in 2012 and 2016, it's clear that there were about 305,000 more Republican votes cast and many of them came from areas known to be Democratic strongholds.
It's also clear that Donald Trump won about 37,000 more votes in Wisconsin that Mitt Romney did and, yet, Mitt Romney won the Wisconsin primary.
This adds up to Dems crossing over.