Head of horticulture Raoul Curtis-Machin said the HTA had pointed out to SNP MPs, who are opposed to change in England and Wales and have prevented legislative progress so far, that some large garden centre companies are Scotland-based.
He said: "We still want to present our case that garden retail is sufficiently different from regular retail that it warrants a special case like farm shops."
The brochure said "relaxing existing trading rules will benefit the garden industry" and said those rules "target" large retailers over 280sqm.
It said Sunday opening would "extend family, leisure and community time" and staff would be protected.
Online retail's threat and a potential £75m gain for garden centres are detailed.
The brochure said garden centres are "easily defined" as 92 per cent have more than a fifth of their selling area outside for plant sales.
The HTA says it has based its analysis on Dobbies and Klondyke centres, both of which operate in Scotland and England. It found some staff still work on Easter Sunday, even where trading is banned, for instance to turn customers away. One chain of seven English centres is cited as having turned away 1,872 cars away on Easter Sunday.