Unionization Rates and the "Demand for Unionization" in North America

Stats Canada’s latest numbers are out on unionization in Canada. They show that the unionization rate in Canada rose last year from 29.5% to 29.6%, which is about 4.2 million union members out of about 14.3 million employees.   Women’s share of the unionized workers continued to grow.  The percentage of women who are unionized is now about 31%, while the percentage of men in unions is close to 28%.   Much of that story is explained by differences between the public and private sectors.  The percentage of unionized women in the private sector is 12.7% (compared to 19.2% for me), but it is 73% in the public sector (compared to 67.5% for men).
Does the fact that 29.6% of Canadian employees are unionized mean that about that percentage are supportive of unions?
This is a question examined in a book by a former professor of mine, Noah Meltz (who passed away a few years ago) and Professor Lipset called The Paradox of American Unionism.  Here’s some of the results of their surveys of American and Canadian workers:
Percentage of Unionized Workers Who  Would Vote to Remain in the Union if Asked to Vote:
U.S.:   90.5%        Canada:  85.8%
These numbers indicate that 9.5% of American union members and 14.2% of Canadian union members are what the authors call “unwilling union members”.  That is, they are in a union but would prefer not to be.   The vast majority of union members would choose to remain union members if given the choice to leave.
Percentage of Non-Union Workers Who Would Vote for a Union if Given the Opportunity
U.S.:    48.2%        Canada:   33%
That’s a remarkable statistic.  It means that about half of non-union American workers, and one-third of Canadian workers would like to be in a union, but can’t get access to one.
Total Percentage of Workers Who Would Like to Be in a Union or to Remain in a Union
U.S.    55%       Canada:  52%
These statistics certainly challenge the perspective often presented in the business media that most people believe that unions are unnecessary and are opposed to unions.  There is still quite strong support for unions, it turns out.
Keep in mind that the unionization rate in the U.S. is about 16%, compared to about 30% in Canada.   The authors of the book conclude that almost all of the difference between unionization rates in Canada and the U.S. (90 percent of the difference) is explained by “supply side” factors.  This means that the explanation lies in much greater “frustrated demand” for unionization in the U.S..    Something is preventing American workers from accessing collective bargaining to a higher degree than Canadians.
What could that be?
A usual explanation is that the legal model in Canada gives greater protection for the right to unionize than the American model.  It is much easier for American employers to interfere with the ability of workers to opt for collective bargaining, for a variety of reasons.
If over 50% of workers want to be unionized, but only 16% (U.S.) and 30% (Canada) are unionized, does this mean to you that there is a failure of the legal model facilitating union organizing?  Should the state change the model to make it easier for those workers who want a union to unionize?  Or, is “frustrated union demand” not a problem that the state should worry about?