From the Keukenhof website:
https://keukenhof.nl/en/
"Combitickets will be available from mid-February. Keep an eye on our website. With public transport you travel quickly and comfortably to Keukenhof. Buy a combiticket to get both your entrance ticket for Keukenhof and the ticket for your journey by public transport on that day. More information will follow shortly.:
THIS is what I'll do if I decide to go to Keukenhof when I am in Amsterdam in April.
I recommend that you do not book tours thru Viator which is a 3rd party consolidator of tours and is owned by Trip Advisor. They charge the provider 20-25% of the ticket price to broker a tour so it's better if you can book directly with the company providing the tour such as the link above to Keukenhof.
There are tons of canal boat tours. A lot of people do Those Dam Boat Guys (I think Rick likes them) although I've never done one of their boat rides. I'm not sure if the canal boats in Amsterdam go on a set route like the ones in Bruges and Ghent.
Since you are going in April, there is also a special Vermeer Exhibition on at the Rijksmuseum for which you will need to book ahead if it's of interest to you.
https://www.rijksmuseum.nl/en/whats-on/exhibitions/vermeer