Canova won't challenge Nelson. No one wants to be responsible for the Democrats losing ground in the Senate in 2018.
Nelson wins because he still racks up majorities in Brevard County, where the Kennedy Space Center is located. Nelson's from Brevard, which now has 500,000 people and is a likely R county in most every election. While most folks see Nelson as a typical National Democrat, some in Brevard remember when Nelson was a rather conservative Democrat who was once approached about switching parties.
It was around 1988 that Nelson really committed to being a Democrat. His friends in Brevard's Democratic Party were Al and Patsy Kurth. Al was a fundraiser, and Patsy was a State Senator, and a cousin of Dick Gephardt, who Nelson was close to in Congress. Nelson hasn't been viewed as a liberal throughout his career, and this serves him in good stead at times. He's in less trouble than folks think.
I'd also add that he's well regarded for his military advocacy up in DC and has done better than the average democrat in places with strong military presence like Bay, Escambia, and Duval. I'd expect that to continue as well.
